Piezoelectric drive

ABSTRACT

A piezoelectric drive having an excitation piezoelement ( 10 ) and a resonator ( 2 ). The resonator is coupled to the piezoelement and is in interactive connection with a body ( 3 ) to be driven. The resonator ( 2 ) has a mass distribution that is designed such that, as a result of an excitation oscillation by the piezoelement ( 10 ), the resonator ( 2 ) begins to asymmetrically oscillate in several directions dependent on the frequency of the excitation oscillation. The asymmetric oscillations, via the interactive connection, displace the body to be driven into a directed movement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to piezoelectric drives, to piezoelectricresonators for drives and to the use of piezoelectric drives as well asto piezoelectric resonators.

2. Description of Related Art

Certain, so-called piezoelectric materials may be excited intomechanical oscillation by applying an electrical alternating current.This physical effect is also called the reverse piezoelectrical effect.A known use of this effect is the use of piezoelectric materials asoscillation exciters in resonators. Such piezoelectric resonators may beinstalled into drives in order to drive rotatably mounted rotors.

The drives that are known in the art and that are based on thepiezoelectric effect have severe disadvantages, which until today haveprevented a widespread industrial use as drives. A complex actuation ofthe piezoelectric oscillation elements, a large danger of contamination,very small mechanical tolerances that prevent a trouble-free operationand a poor efficiency are the most severe disadvantages. Furthermore,with the solutions known today only very low rotational speeds with anextremely small torque are possible. A reduction in size of these drivesso that they may be used, for example, in micro-technology or medicaltechnology or also in the field of clocks is possible only at a greatexpense, rendering economical manufacture impossible. The largemechanical abrasion of the known arrangements further demand the use ofparticularly hard, and therefore expensive, materials that are difficultto machine. Only a small amount of abrasion causes an increase of theplay and a contamination of the drive, which inevitably leads to afailure after a short operational duration.

Such piezoelectric drives are, for example, disclosed in the documentsEP-0,505,848 (hereinafter referred to as EP'848), EP-0,723,213(hereinafter referred to as EP'213) and FR-2,277,458 (hereinafterreferred to as FR'458) as well as the document equivalent to this DE 2530 045 (hereinafter referred to as DE'045).

EP'848 and EP'213 show multi-part centrally arranged piezoelectricresonators with two or three resonator wings. The ends of the resonatorwings have abutments for abutting rotors, which are arranged annularlyon the outside around the resonators. With these piezoelectric drivesthere is the disadvantage of the abrasion at the abutment surfaces ofthe resonator wings and at the capture surfaces of the rotors as well asthe bearing play of the rotors. The abrasion results in a high wear,which shortens the life duration of the piezoelectric drives and limitsits potential field of application.

DE'045 (corresponding to FR'458) describes the most varied ofarrangements of electrical motors that are based on piezoelectricelements. These motors have a stator and a rotor, wherein at least oneor both has a vibrator that encloses a piezoelement. The stator and therotor are pressed against one another at a point of the surface thatlies on the surface of the vibrator by way of an elastic element inorder to transmit a moment. A direction change is effected by way of areversal means, which functions to the extent that several vibrators arealternately applied. In DE'045 it is mentioned that with these motorswith a resonator it is impossible to change the rotational direction. Achange of the rotational direction demands two vibrators (for examplerotor and stator active). Furthermore, the abutments perpendicular tothe contact surface between the rotor and the stator aredisadvantageous. It is mentioned that the wear with the motors is verylarge, in particular with several rotational directions. A reversal ofthe rotational direction is only achieved at a great expense. On accountof the parts, which are very difficult to manufacture, a suitable designis very expensive.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide apiezoelectric drive that has a low wear, is inexpensive, and ismanufacturable in any size, particularly small and flat. The drive is tobe robust in operation, simple in maintenance and large in power. It isto have a large rotational speed range in several rotational directionsand, furthermore, permit a simple position determination. Thispiezoelectric drive is to be compatible with common standards.

Piezoelectric drives are, as a rule, based on resonators that are setinto oscillation. These are, in turn, transmitted to a body to bedriven. The present invention is based on the recognition that theoscillation behavior of a piezoelectrically excited resonator may beinfluenced in the longitudinal direction as well as the transversedirection by way of a targeted design and arrangement. Apiezoelectrically driven resonator operated in a mix mode by way of thedesign of the present invention permits a body to be set into motion.According to the shaping of the resonator and the arrangement of one ormore resonators to a body, a variety of structural embodiments and usesbecome possible. By way of the special design, several dominantoscillation forms may be excited. By way of the special design, it ispossible to select the. oscillation forms such that the rotationaldirection amongst other things may be selected dependent on thefrequency. An influencing of the rotational speed is advantageouslyeffected by way of the magnitude of the amplitude. Due to the inventiveshaping of the resonator, it is further possible to minimize damagingvibrations that cause wear. By way of a directed arrangement it isachieved that abrasion does not have a negative effect and iscompensated. The piezoelectric drive may be used for the unidirectionalor bi-directional drive of bodies, such as shafts and disks, with onlyone piezoelement. In contrast to this, the state of the art arrangementsas a rule require several oscillation quartzes, which must be exactlycoordinated to one another.

In an advantageous solution a longitudinal oscillation component of thepiezoelectric resonator serves for driving a body while a transverseoscillation component of the resonator exerts a temporary pressure onthe body. By way of the thus created pressure angle large forces may betransmitted onto the body to be driven. The drive, when required, has agreat self-locking so that, among other things, the body is held. Anadditional mounting of the parts to be moved may be avoided in adirected manner.

The piezoelectric drive according to the invention comprises anexcitation element and a resonator that is coupled to the excitationelement and in interactive connection with a body to be driven. Theexcitation element is advantageously mounted between two parts of theresonator and acts indirectly on the body to be driven. The movementinduced by the excitation element is transformed by the resonator andthen transmitted to the body to be driven. The resonator has a massdistribution, which is configured such that, as a result of anexcitation oscillation by way of the excitation element, dependent onthe frequency of the excitation oscillation, the resonator begins tooscillate asymmetrically in several directions. These oscillations, viaan interactive connection, are transmitted onto the body to be drivenvia the interactive connection so that this is set into a directedmovement. The mass inertia of the oscillating elements is exploited in adirected manner in order to produce advantageous oscillation forms, Byway of the arrangement and design it is achieved that the excited formsof movement achieve an optimized drive with a minimal of wear andmaterial loading. By way of adjustable elements it is achieved that anyoccurring incidences of wear are compensated and equalized. Theresonators are advantageously excited with a frequency that correspondsto frequency of resonance or of a multiple thereof. A resonator as arule comprises severally differently and asymmetrically formed armsthat, depending on the frequency of excitation, oscillate differently.These are also influenced by way of the material choice and the massdistribution.

The movement form of the resonators is selected such that one achieveshigh resonance frequencies and, thus, large rotational speeds. Incontrast to the state of the art, the drive according to the inventionfunctions at very high frequencies and the piezoelements may also beselected small. The resonators are constructed so that they permit modesof oscillation. The drive according to the invention is very robust andhas large cooling surfaces. A negative, perpendicular abutting of thepiezoelements onto the surface of the part to be driven is avoided in adirected manner, in particular before the drive begins to act. The massand its distribution of the resonator and its pressing force play animportant part. In order to achieve a high efficiency and a large torqueit is important for the driving elements to carry out as much work aspossible during the time.

In a preferred arrangement, the drive has a single piezoelectricresonator with which one drives bi-directionally. This, among otherthings, permits a simple activation of the resonator and piezoelectricdrive over a single oscillation with the same frequency and phase. Forexample, in order to realize a particularly small drive it is possibleto integrate the piezoelectric element, which is responsible for themechanical excitation, into the oscillation circuit as an activeelement. By way of this structure, together with a drive for a clock,one would be able to do away with additional oscillation quartzes.Corresponding arrangements are also particularly advantageous in medicaltechnology.

A ratio of the length to the width of the exciter, in thepiezoelectrically driven resonator, equal to two or a multiple thereof,is particularly favorable. The body to be driven is driven with amaximum amplitude, which results in an optimal efficiency of the drive.

The piezoelectric drive, when required, is provided with positioningmeans, which are formed such that they create a signal that may beexternally measured. For example, by way of an alternating pressingforce of the piezoelectric drive one may achieve changes in impedancethat are measurable and countable. Thus, a position detection of thebody is possible which, for example, permits the use of the drive as astepper motor. Also, in clocks a corresponding positioning aid may beuseful, e.g. for setting the hands to zero.

The resonator and the excitation element by way of an elastic means areadvantageously mounted elastically with respect to the body to bedriven. The elastic mounting compensates for malfunctions occurring ondriving the body and, among other things, leads to a very smooth runningon the drive. Also any wear occurring by way of abrasion on the drivesurfaces and capture surfaces is compensated. The elastic means may, forexample, be designed as a spring. By way of material selection andarrangement one may influence the spring and/or damping behavior.Advantageously, the elastic means may, at least in one direction, have asmaller elasticity than the interactively connected resonator. Theelastic means is, in particular, designed such that it does notunintentionally transmit movements (oscillations). The elastic elementand the resonator may also be designed as one piece and be of the samematerial. Therefore, the function of the elastic element and resonatoris then defined by shaping and arrangement. The elastic means may be onepiece or several pieces. For example, springs of metal or plasticelements that are manufactured, for example, by injection molding aresuitable.

The piezoelectric drive may be designed very flat and be used as arotation or linear motor. The most varied of applications are possible.Exemplary fields of application are clocks, cameras, data memories,microscope tables, tachos, etc.

The resonators, which as a rule are driven by way of piezoelectricelements, may, for example, be particularly advantageously manufacturedby way of injection molding. The piezoelements at the same time are, forexample, applied into the mold and then further plastic is injectedtherearound. Accordingly, it is suitable to integrate an elasticmounting. Another variant lies in pressing and/or sintering the parts.Adhesive or mechanical connections, depending on the size of the drivelikewise lead to success.

The resonators are advantageously designed as one piece and have a shapesuch that as a result of the mass distribution and arrangement one mayexcite suitable oscillation patterns and forms. By way of materialselection, design and mounting, the oscillation patterns to be excitedmay be set dependent on the frequency. The design is selected such thatdepending on the excitation frequency one may excite differentoscillation forms, permitting direction changes to be produced. Thedrive speed is preferably set via the amplitude of deflection. Theinertia of the mass is exploited in a directed manner. By way of this itis possible, with a given excitation frequency, to operate at differentdrive speeds by variation of the amplitude. On driving the shaft,rotational speeds of a few to a few thousand rotations per minute arepossible. By way of the selection of the mounting or suspension of theresonator relative to the body to be driven, one may set the pressingforce, the holding moment and further variables. The resonator has anindirect or direct, active or passive interactive connection to the bodyto be driven. The mounting of the resonator with respect to the body tobe driven compensates for wear and inaccuracies.

The movement of the oscillating parts of the drive according to theinvention may be described simplified as follows: a longitudinaloscillation caused by an exciter in a resonator effects secondaryoscillation modi (e.g. the transverse modi). The secondary or transverseoscillation modi sets in after a certain delay since, among otherthings, on account of the mass inertia and elasticity of the material itrequires some time until the resonator moves into another oscillationmode. In other words, the speed of sound in a resonator and thebordering regions determines the delay time. By way of this (ontransition from a longitudinal into a transverse oscillation mode bysuperposition) there is created an oscillation form similar to anellipse. Dependent on location there are regions on the resonator thatoscillate with a different “orientation”, depending on the frequency andamplitude. If for example, corresponding regions are brought intointeractive connection with a rotor, a force is transmitted onto this sothat this begins to move accordingly. A drive according to the inventionin a typical manner is operated with an excitation frequency of 50 kHzto 500 kHz depending on the size of the resonator and the speed of sound(with a suitable dimensioning other operating conditions are likewisepossible).

Exciters may consist of any known piezoelectric materials includingpiezoelectric crystals, ceramics, plastics, etc. The oscillation bodiesmay consist of any material, such as metal, plastic, etc. The connectionof the exciter or exciters to the oscillation bodies is effected via aknown frictional fit, material fit, or positive fit means. With theknowledge of the present invention varied possibilities of connectingthe exciter to the oscillation bodies are available to those skilled inthe art. For example, exciters of ceramic with oscillation bodies ofmetal are attached with component adhesive.

With certain embodiments a ratio of length to width of the exciter equalto two or a multiple thereof is advantageous. A ratio of length to widthequal to 2n(n=1, 2, 3, . . . ) leads to particularly high amplitudes inthe exciter.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further features of the invention will be apparent withreference to the following description and drawings, wherein:

FIG. 1 is a perspective view of a first embodiment of a piezoelectricdrive with a resonator and a contact location;

FIG. 2 is a perspective view of a second embodiment of a piezoelectricdrive with a resonator and two contact locations;

FIG. 3 is a perspective view of a third embodiment of a piezoelectricdrive with a resonator and two contact locations;

FIG. 4 is a perspective view of a fourth embodiment of a piezoelectricdrive with a resonator and two contact locations;

FIG. 5 is a perspective view of a fifth second embodiment of apiezoelectric drive with three resonators and six contact locations;

FIG. 6 is a perspective view of an embodiment of a piezoelectric drivefor a clock with two hands;

FIG. 7 illustrates an embodiment of a piezoelectric drive for a shaft;

FIG. 8 schematically shows a piezoelectric drive;

FIG. 9 illustrates a further embodiment of a piezoelectric drive;

FIG. 10 illustrates a sandwich-like arrangement of the piezoelectricdrive according to FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically and greatly simplified shows a perspective view ofa piezoelectric drive 1 with an essentially sickle-shaped resonator 2,with a round rotor 3, a spring element 4, and a holding device 5. Theresonator 2 here consists of a piezoelement (excitation element) and twooscillation bodies 11, 12 attached to this on the end face. Theresonator 2 is fastened on the holding device 5 by way of the springelement 4. The rotor 3 is rotatably mounted on the holding device 5about the pivot 13. The resonator 2 is in interactive connection with asurface 20 of the rotor 3 by way of a contact element 14. The holdingdevice 5 and the pivot 13 are here connected by snapping-in. Uponapplication of a suitable voltage to the piezoelement 10, thepiezoelement 10 is displaced into oscillation, which is transmitted tothe coupled oscillation bodies 11 and 12. By way of the special designand mounting of the resonator 2, the multi-dimensional oscillationsexcited by the piezoelement 10 superimpose such that the contact element14 executes a cyclic drive movement, which is transmitted dependent onthe frequency and amplitude onto the surface 20 of the rotor 3. Theresonator 2 is designed such that the movement of the contact elementextends essentially parallel to the surface to be driven, withoutdamaging the surface. The form of the movement of the contact element isdependent on the configuration of the material properties (E-module,density, etc.), on the frequency and amplitude, and on the mounting,particularly mounting of the rotor 3. The rotor 3 influences themovement of the resonator 2. By way of this it is possible to find anoptimal solution depending on the demands set. The dependency on theadjustable parameters extends so much that the direction of the drivemay be varied in a directed manner. For example, by changing thefrequency, the movement of the contact element 14 may be changed suchthat the rotational direction of the rotor 3 changes. The spring element4 is formed such that it interactively takes part in the movement of theresonator 3. The mounting of the resonator 2 with respect to the rotor 3is selected such that changes, such as any occurring abrasion andthermal expansions, are compensated. The mounting of the resonator mayalso be actively designed in a manner such that further influences maybe exploited. In particular, the mounting is supported by way ofdamping, so that oscillation forms may be influenced in a directedmanner.

The piezoelement 10 is excited by the spring elements 4 laterallyattached on both sides in that an electrical voltage is applied. By wayof this it begins to oscillate in a first oscillation in the directionof the oscillation bodies 11, 12 attached on the end face and,perpendicular to this, in a second oscillation and has the effect thatthe resonator 2 is displaced into characteristic oscillation.Simultaneously, secondary oscillations superimpose. The spring element4, which is essentially s-shaped, is at the same time designed such thatit behaves in a neutral manner with respect to the excited oscillationand supports transmission of this oscillation to the body to be driven.The spring element 4 is designed such that it has an increasedflexibility at least in one direction so that the resonator may be movedin this direction in a preferred manner. The resonator 2 is essentiallysickle-shaped and has mass concentrations at defined locations. Thedesign of the resonator 2 (including the excitation element 10) effectsthe preferred drive movement.

The movement of the contact element is shown greatly simplified indetail D. The movement that sets in as a result of the multi-dimensionalsuperimposing oscillations of the driving piezoelement 10, and by way ofthe design of the oscillation bodies 11 and 12, is indicatedschematically by an arrow 23.1. The speed of the contact element 14varies in dependence upon the location and the amplitude of theexcitation oscillation. The speed is set by way of a change of theamplitude of the excitation oscillation. An oscillation which sets in asa result of a smaller amplitude is shown schematically by an arrow 23.2.The movement of the resonator about the pivot 13 is shown schematicallyby an arrow 20.

With the arrangement shown here the rotor 3 may be latched very simply.It is firmly held by the rotor 2 positioned over the spring element 4.

FIG. 2 shows in a schematic and simplified manner a further embodimentof a drive 1. The individual parts corresponding to those of FIG. 1 willnot be described in detail again. The arcuate resonator 2 apart from thepiezoelectric element 10 comprises two t-shaped or I-shaped designedoscillation bodies 11, 12, which connect to the piezoelectric element 10on the end face and each comprise one contact element 14, 15. Thesecontact elements 14, 15 are in interactive connection with the surface20 of the rotor 3. The spring element 4, which here is s-shaped, isattached on a side of the piezoelement 10 facing the rotor 3, asillustrated. The spring element 4 serves as an elastic mounting of theresonator 2 with respect to the holding device (chassis) 5, and servesfor transmitting the reaction forces that arise on account of the drivemovement transmitted onto the resonator 2. The spring element 4 isdesigned to ensure the interactive connection between the contactelements 14, 15 and the rotor 3. The spring element 4 has an increasedspring force.

The excitation of the piezoelement 10 with a supply voltage is hereeffected via separate connections (not shown in more detail). Thepiezoelement 10 by way of this begins to oscillate in the direction ofthe oscillation bodies 11, 12 attached at the end face, and in adirection perpendicular to this.

The rotor 3 comprises elements along its circumference, here in the formof distanced deepenings or grooves 21. These elements 21 permit theproduction of count impulses so that the position of the rotor may bedetermined. The grooves 21 are designed in a manner such that preferablyin the resonator 2, for example in the piezoelectric element 10 a changeof a measurable variable is created. With this it may be the case of animpedance change, which is detected externally and analyzed. In place ofgrooves, other means that would lead to an equivalent result are alsoconceivable (for example special shapes of the resonator). Thepositioning means or grooves 21 are designed such that they do notnegatively inhibit the functioning manner of the drive and such that theposition of a body may be determined by way of the change of onemeasurable variable, in particular impedance changes. The maximumdriving torque may be determined by the dimensioning of the parts. If,for example, the diameter of the rotor 3 is increased, the drivingtorque increases. The holding torque may be set by way of the element 4and via the friction. If required, additional elements for increasingthe holding or driving torque are possible. The drive may for examplealso be coupled to a gear in order to meet special demands.

FIG. 3 shows a further embodiment of the drive 1. The drive has anapproximately u-shaped resonator 2 with two oscillation bodies 11, 12that are connected to a piezoelement 10 on the end face. The oscillationbodies, which have different thickness, are in interactive connectionwith a side surface 20 of the rotor 3. More specifically, theoscillation bodies 11, 12 are in contact laterally to side surface 20 ofthe rotor, essentially tangentially. The resonator 2 is fastened on aholding device 5 such that its drive movement is not negatively impeded.One may influence the oscillation form of the resonator by way of thetype and manner of the fastening. Depending on the applied type, thepiezoelement 10 is excited either in the region of the end faces or atthe free side surfaces, so that it begins to oscillate in the region inthe direction of the oscillation bodies attached on the end face. Onaccount of the design and arrangement of the resonator 2, the secondarymovements superimpose, resulting in a directed drive movement.

The rotor 3 is rotatably mounted on the holding device 5 about a pivot13. The shaft 13 in the illustrated embodiment is arranged in the centerof the rotor 3. The number of oscillation bodies 11, 12 is not limitedto two and is determined depending on the operational requirements.Other solutions deviating from the embodiments shown here, in which, forexample, more than one rotor 3 is drivable, are also conceivable. Onemay also realize resonators 2 with more than one exciter and with morethan two oscillation bodies. For example, the resonator 2 consists of aplurality of exciters or oscillation bodies 11, 12, which are present ina multilayer construction.

The oscillation bodies 11, 12 are designed such that they drive therotor 3 in a frequency-dependent manner. The speed is determinedadvantageously via the amplitude. It is possible for one skilled in theart to find suitable solutions with the knowledge of the inventiondisclosed here. With other embodiments the pivot 13 may be arrangedeccentrically with respect to the rotor 3 such that in the piezoelement10 there is created a measurable change dependent on position. The shapeof the rotor 3 in not necessarily circular, but it may, for example, beoval-shaped in order to create a suitable change. The piezoelement 10may also have at its disposal more than one connection pair for excitingthe oscillations. The parts here designed stationary may of course alsobe movably arranged. The same also applies to the movable parts: forexample it is possible to integrate the resonators into a rotor or notto arrange these stationarily.

FIG. 4 shows a further embodiment of the drive 1 schematically andgreatly simplified. A rotor 3 is here designed as an annular hollowrotor and is mounted only by two differently long oscillation bodies 11,12, which in the contact region run essentially tangentially to therotor 3. The oscillation bodies 11, 12 are attached to two oppositelylying surfaces of a piezoelement 10 on the end face and together withthis piezoelement form a u-shaped resonator 2. A holding device 5 ishere interactively connected to the resonator 2 and serves as theresonator mounting. The oscillation bodies 11, 12 are designed tooscillate anti-cyclically as a result of a mechanical excitation by thepiezoelement 10 and in combination with the rotor 3. The oscillationbodies 11, 12 have a certain pretension with respect to the rotor 3, bywhich means this is rotor is held and the drive movement is transmitted.Longitudinal oscillation components in the resonator 2 drive the rotor 3tangentially, transverse components exert a holding and centeringpressure on the rotor body. The rotor 3 is held by elastic means. Largeholding forces are possible so that no further or external bearings arenecessary for mounting. The conveyed torque may be very large since thestep angle of the rotor body per oscillation is very small. For example,the step angle is 0.01°.

FIG. 5 schematically shows the drive 1 with three arcuate resonators2.1, 2.2, 2.3. With this embodiment, which is essentially a parallelconnection of three resonators according to FIG. 2, an increase in thedrive power is achieved. Each of the three resonators 2.1, 2.2, 2.3 haveone piezoelement 10.1, 10.2, 10.3 that is connected at the end face ontwo essentially parallel opposite sides to an oscillation element 11.1,11.2, 11.3, 12.1, 12.2, 12.3. The oscillation elements are formedarcuate and I-shaped so that they have a mass distribution which leadsto the desired oscillation behavior. With the three resonators, theillustrated embodiment includes three functionally dependent drives.

The resonators 10.1, 10.2, 10.3 are resiliently fastened to a holdingdevice 5, which is annular, by way of spring elements 4.1, 4.2, 4.3. Anannular rotor 3 is centrally mounted by the resonators 2.1, 2.2, 2.3. Byway of an excitation the piezoelements 10.1, 10.2, 10.3 and theoscillation bodies interactively connected to them begin to oscillate ina multidimensional manner. These oscillations superimpose and aretransmitted to the rotor 3, by is therefore set in motion. Play andabrasion are avoided on account of the compensatingly acting mounting byway of the spring elements 4.1, 4.2, 4.3. The spring elements 4.1, 4.2,4.3 are designed in a manner such that they damp amongst other thingsnegative oscillations or these negative oscillations do not have anegative effect on other components. By way of the elastic mounting ofthe rotor 3 shown here, the drive is particularly insensitive to impactloadings.

FIG. 6 shows two drives 1.1, 1.2 produced according to the embodiment ofFIG. 5 that are arranged behind one another. These two drives, forexample, serve to drive two hands 30, 31 as they are employed in clocks,in particular wrist watches or other display apparatus. The first drive1.1 has a pivot 28, which passes through the second drive 1.2 and servesfor mounting the first hand 30. The second drive 31 has a pivot 29designed corresponding through-going, which serves for mounting thesecond hand 31. By way of the arrangement shown here, two hands, as forexample are present in watches, may be actuated independently. By way ofthe design of the drive one requires no gearing and no other mechanicalparts. The hands are furthermore protected from knocks and othermechanical loading. The drives may be designed very small. On account ofthe flat construction it is possible to arrange them behind one another.Amongst one another they have no negative influence and malfunctioning.On account of the very high oscillation frequency the drive ispractically noiseless. Two deepenings or grooves 25, 26 here serve as apositioning means of two rotors 3.2, 3.2. The grooves 25, 26 aredesigned to create a measurable change in one or all resonators 10.1,10.2, 10.3, preferably in the behavior of the piezoelements 10.1, 10.2,10.3. this may be measured externally and serves for positioning thehands 30, 31. In place of the grooves 25, 26 one may also use otherpositioning means. For example the shape of the resonators 3.1, 3.2 maybe selected accordingly.

FIG. 7 schematically shows a further embodiment of a drive 1. The drive1 here acts on a shaft 35. Resonators 2.4, 2.5, 2.6, 2.7 are arrangedaround the shaft 35 and are in interactive connection with the shift 35.The resonators 2 are fastened on a holding device 5, which here isannular, by way of spring elements 4 and each have a piezoelement 10with two coupled oscillation bodies 11, 12. The resonators 2 here areconnected essentially parallel and would also function as functionallyindependent drives. An increase in the power is achieved by way of theparallel arrangement. By way of changing the excitation frequency onemay influence the direction of the movement. The speed is controlled viathe amplitude of the amplitude of the excitation frequency. By way ofsuitably arranged resonators (not shown in more detail) it is alsopossible, apart from an axial displacement, to also achieve adisplacement in the circumferential direction. The number andarrangement of the resonators 2 is not fixed and may be optimized tomeet the demands. When required, it is also useful to provide severalresonators in a different direction so that one achieves directionindependence.

Electrical connections for the supply voltage have not been drawn intothe Figures for reasons of clarity and to provide a better overview. Theresonators themeselves may form the electrical connections when usingelectrically conducting resonator elements. By applying an electricalalternating voltage a resonator is excited into mechanical oscillation.For example, a resonator is excited with a sinusoidal alternatingvoltage of 0.1 V and a frequency of 200 kHz. This permits the use of theresonator and exciters that, for example, are arranged in a multilayerconstruction in battery operated apparatus, such as clocks. On accountof the inventive shaping of the resonator the mechanical oscillations inthe resonator propagate differently. This leads to longitudinal as wellas transverse oscillations that superimpose.

FIG. 8 in a greatly simplified manner shows a schematic functional modelof a piezomotor 1 according to the invention. The motor 1 shown herecomprises a resonator 2 on which there is coupled a piezoelement 10. Thepiezoelement 10 serves as an exciter and is in interactive connectionwith the resonator 2, or is a part of the resonator. An elastic element6, which here is in the form of a spring that is thin in one directionand curved several times, serves for mounting the resonator 2 withrespect to the holding device 5. The elastic element 6 is designed to bepreferably elastic with respect to movements parallel to an x/y-plane.Any occurring abrasion and play as well as undesired expansion are thuscompensated. The resonator 2 has an asymmetrical mass distribution. Fora better understanding this is made clear in a simplified manner byregions 10, 16, 17, 18 with mass concentrations (the piezoelement 10here likewise represents a region with a mass concentration whichinfluences the form of the excited oscillations). The regions with massconcentration 10, 16, 17, 18 are interactively connected via transitionregions 7, 8, 9, whose mass and inertia are assumed to be negligible inthis model. Here the transition regions 7, 8, 9 are formed more thicklyin the z-direction and, due to this constructions, the resonatorpreferably moves in the x/y-plane.

The interactive connections that are shown schematically by arrows 48,49, between the regions with mass concentrations 10, 16, 17, 18 are suchthat the movements of the regions with mass concentrations 10, 16, 17,18 superimpose in a targeted manner and are influenced. The resonatorhere preferably oscillates in the x/y direction, as mentioned above.Secondary oscillations are possible. In particular the inertia of themasses, the elasticity of the material, the damping and the speed ofsound play a significant role. The resonator 2 as a whole has preferredoscillation forms. The regions with mass concentration 10, 16, 17, 18are arranged such that an oscillation that is excited in one directionhas the result that an oscillation is excited in another direction. Byway of this working principle one succeeds with one excitation element10 that produces several drive directions. The direction of theexcitation oscillation is exploited in a targeted manner in that thepiezoelement is arranged according to its direction of preference.Furthermore, in its entirety one achieves the formation ofcharacteristic (standing) forms of oscillation that may be changed andset in a targeted manner by way of the frequency and amplitude of theexcitation. This driving movement is location-dependent and here, by wayof a suitably arranged contact element 14, is transmitted onto a rotor 3to be driven. The drive directions of the rotor are schematically shownby arrows 36, 37. The bearing element 6 is designed such that itsupports the oscillation forms of the resonator 2 or at least does notnegatively influence these. Play and abrasion are compensated with suchan arrangement. The movements of the resonator 2, for the sake ofsimplicity, are limited to regions with mass concentrations and areshown schematically and greatly generalized by way of arrows 40, 41, 42,43, 44, 45, and 46. Arrow 40 schematically represents the excitationoscillation. The resulting movement, which effectively sets in(superposition of the movements represented by the arrows 40, 41, 42,43, 44, 45, 46) is determined by the design (in particular the massdistribution) of the resonator 2 and its mounting or damping. Thedriving movement of the resonator 2 is adjustable via the excitationfrequency in a manner such that the drive direction may be changed. Theresonator is designed such that, by way of an increase or reduction ofthe excitation frequency, another oscillation form may be set (incertain cases this may also be compared to standing waves) so that thedrive movement of the contact element 14 changes. The interactiveconnection between the contact element 14 and the rotor 2 is selectedsuch that the movement of the rotor is not negatively influenced. Theresonator and the bordering parts are manufactured as one piece whenrequired. As is shown in the above-described embodiments, it is possibleto realize more than one driving contact point between the resonator 2and the body to be driven. A suitably favorable design of the resonator2 makes this possible. By way of a suitable selection of the massdistribution and interaction, several contact regions of the resonator 2drive the rotor 3 in the same direction. The direction of the drive isdetermined by way of a suitable setting of the excitation frequency. Byway of the amplitude of the excitation oscillation the speed may be setin a targeted manner. With the knowledge of the invention disclosed hereit is possible for one skilled in the art to accordingly create otherarrangements and designs of resonators.

FIG. 9 shows a further embodiment of a piezoelectric drive 1 in a verysimplified and schematic manner. One may recognize a piezoelement 10that is coupled between two flat oscillation bodies 11, 12 that in crosssection are in the shape of a truncated pyramid. The oscillation bodies11, 12 here are no longer attached on the piezoelement 10 on the endface, but rather laterally of the end face. The resonator 2 is mountedvia spring elements 4.1, 4.2 (the other side of the mounting is notshown in more detail). The oscillation bodes here are in interactiveconnection with a rotor 3, which is rotatably mounted about a pivot 47.The two oscillation bodies 11, 12 are designed electrically conductingand serve the activation of the piezoelement 10. The oscillations of thepiezoelement 10 in the longitudinal direction and perpendicular to thelongitudinal direction are transmitted to the oscillation bodies 11, 12.The oscillation bodies influence and transform these movements andtransmit them onto the rotor 3 such that the rotor rotates about thepivot 47. This drive is also suitable as a linear drive.

FIG. 10 shows a possible arrangement of oscillation bodies 11.1, 11.2,11.3, 12.1, 12.2, and piezoelements 10.1, 10.2, 10.3, 10.4 according toFIG. 9. The oscillation bodies 11.1, 11.2, 11.3, 12.1, 12.2 and thepiezoelements 10.1, 10.2, 10.3, 10.4 are here alternately arrangedparallel and mutually support one another in their effect. By way ofsuch an arrangement the transmitted forces are increased. With thisconnection in parallel, in contrast to the state of the art, as a ruleno separate activation of each piezoelement is required. By way of thisthe motor may be operated with little expense.

What is claimed is:
 1. A piezoelectric drive (1) comprising: a resonator(2) that includes an excitation piezoelement (10) and an oscillationbody (11, 12), said oscillation body (11, 12) being coupled to thepiezoelement and being in interactive connection with a body (3) to bedriven, wherein the resonator (2) is mounted via mounting means (4, 6)attached to the resonator and acting elastically with respect to thebody (3) to be driven, and has a mass distribution designed such that,as a result of an excitation oscillation by the piezoelement (10), anddependent on a frequency of the excitation oscillation, the resonator(2) oscillates asymmetrically in several directions (x, y, z), theasymmetric oscillations, via the interactive connection, displace thebody (3) to be driven into a directed movement, and wherein theoscillation body (11, 12) is integrally formed with a spring element (4,6) and may be brought into oscillation via the integrally formed springelement.
 2. The piezoelectric drive (1) according to claim 1, whereinthe spring element forms an electrical connection to the piezoelement.3. The piezoelectric drive (1) according to claim 1, wherein theoscillation body (11, 12) is formed from a material selected from thegroup consisting of electrically conducting material, abrasion-resistantmaterial, and thermally conducting material.
 4. The piezoelectric drive(1) according to claim 1, wherein the resonator (2) has an asymmetricalshape and may be brought into oscillation in a longitudinal mode as wellas in a transverse mode.
 5. The piezoelectric drive (1) according toclaim 1, wherein the piezoelectric drive (1) comprises only onepiezoelement (10).
 6. A piezoelectric drive (1) according to claim 1,wherein the piezoelectric drive (1) comprises a plurality ofpiezoelements (10.1, 10.2, 10.3) that are disposed parallel to eachother and are connected together.
 7. A piezoelectric drive (1) accordingto claim 1, wherein the mounting means (4, 6), with respect to a springeffect, is designed such that there is effected a reduction in the wearbetween the resonator and the drive.
 8. The piezoelectric drive (1)according to claim 1, wherein the piezoelement (10) comprises sidesurfaces and at least one end face, said side surfaces being connectedin an electrically conducting manner to the spring element (4) and saidend face being in interactive connection with the oscillation body (11,12), such that the piezoelement (10) is excited into oscillation in thedirection of the end faces by way of applying an electrical voltage tothe side surfaces, and the interactively connected oscillation body (11,12) is excited into oscillation.
 9. The piezoelectric drive (1)according to claim 1, wherein a speed of the driven body (3) may be setby an amplitude of the excitation piezoelement (10).
 10. Thepiezoelectric drive (1) according to claim 1, wherein a direction ofmovement of the driven body (3) may be set by the frequency of theexcitation piezoelement (10).
 11. The piezoelectric drive (1) accordingto claim 1, wherein the resonator (2) has several interactiveconnections (14) with respect to the body (3) to be driven.
 12. Thepiezoelectric drive (1) according to claim 1, wherein the body (3) to bedriven is a rotor (3) or a linear drive.
 13. The piezoelectric drive (1)according to claim 1, wherein a positioning means (24) produces a changeof a measurable variable, said change in the measurable variableincluding a change in impedance and a change in phase, such that aposition of a body (3) may be determined.
 14. A method for driving abody, said method comprising the steps of: displacing a piezoelectricelement (10) of a resonator into a first and/or second oscillation,transmitting this first and/or second oscillation onto an interactivelyconnected oscillation body (11, 12) of the resonator, elasticallyholding the resonator relative to a body to be driven using a springelement integrally formed with the oscillation body (11, 12) such thatthe oscillation body (11, 12) is displaced into a multidimensionaloscillation, wherein in a certain zone of the oscillation body (11, 12)there is formed a characteristic movement, said characteristic movementincluding an elliptical movement, and wherein said characteristicmovement is transmitted onto the body (3) to be driven so that said bodyis displaced into a directed movement, wherein the oscillation of theoscillation body (11, 12) is brought into oscillation via the integrallyformed spring element, and whereby the holding of the oscillation body(11, 12) using the spring element reduces the wear on the body (3) to bedriven and the oscillation body (11, 12).
 15. The method according toclaim 14, further comprising the step of setting a speed of the drivenbody (3) by setting an amplitude of the excitation piezoelement (10).16. The method according to claim 14, further comprising the step ofsetting a direction of the movement of the driven body (3) by settingthe frequency of the excitation piezoelement (10).
 17. Use of the drive(2) according to claim 1, in a manner such that the drive, either insteps or continuously, sets parts in clocks, cameras, data memories,microscope tables or tachometers into movement.
 18. A piezo electricdrive comprising: a rotor having a contact surface; a resonatorincluding a piezoelement connected to an oscillation body and operableto generate oscillations in the oscillation body, said oscillation bodyhaving a contact element; a holding device that rotatably holds therotor; and an elastic spring element connecting the resonator to theholding device, wherein the spring element conducts electrical voltageto the piezoelement; and wherein the construction of the resonator andthe connection of the resonator to the holding device by the springelement is such that the oscillations of the oscillation body cause thecontact element to move in an elliptical path, during which the contactelement of the oscillation body contacts the contact surface of therotor, thereby causing the rotor to rotate.
 19. A piezo electric drivecomprising: a rotor having a contact surface; a resonator including apiezoelement connected to an oscillation body and operable to generateoscillations in the oscillation body, said oscillation body having acontact element; a holding device that rotatably holds the rotor; and anelastic spring element connecting the resonator to the holding device;and wherein the construction of the resonator and the connection of theresonator to the holding device by the spring element is such that theoscillations of the oscillation body cause the contact element to movein an elliptical path, during which the contact element of theoscillation body contacts the contact surface of the rotor, therebycausing the rotor to rotate; wherein the resonator further comprises asecond oscillation body, and wherein the piezoelement is connectedbetween the oscillation body and the second oscillation body.